The present invention generally relates to multiple picture composing methods and multiple picture composing apparatuses, and more particularly to a multiple picture composing method for composing a plurality of pictures and transmitting a composed picture and to a multiple picture composing apparatus which employs such a multiple picture composing method.
In video conference systems, remote monitoring systems and the like, it is known to transmit a plurality of pictures and to make a multiple picture display at a receiving end. In this case, video signals can be transmitted as they are if a high-speed transmission channel can be used as a transmission path. But normally, a low-speed transmission channel is generally used as the transmission path, and the video signals must be compressed, encoded and transmitted. The systems may be categorized into a type which synchronizes and processes the video signals from a plurality of picture pickup apparatuses, and a type which processes asynchronous video signals. The system of the latter type has a simpler and less expensive construction. Accordingly, there are demands to efficiently compose multiple pictures of asynchronous video signals.
FIG. 1 is a diagram for explaining a synchronous video signal composing remote monitoring system which includes television cameras 201, a multiple picture composing apparatus 202 having a synchronizing signal distributor 202a, a transmission unit 203 having an encoding function, a network 204 such as a radio satellite line, ISDN, ATM network and LAN, a transmission unit 205 having a decoding function, and a monitor 206.
The 4 television cameras 201 respectively pickup pictures of objects to be monitored, namely, a volcano, a river, a power line and a factory, by carrying out horizontal and vertical scans based on synchronizing signals from the synchronizing signal distributor 202a. Hence, video signals #1, #2, #3 and #4 which are output from the television cameras 201 by picking up the corresponding objects to be monitored are synchronized, and the multiple picture composing apparatus 202 composes the video signals #1 through #4 based on the synchronizing signals to input a composed video signal to the transmission unit 203.
The transmission unit 203 compresses, encodes and transmits the composed video signal depending on a transmission band and the like of the network 204. The transmission unit 205 receives the compressed and encoded composed video signal via the network 204, and restores the original composed video signal by carrying out a process complementary to that at the time of the compression and encoding. The restored original composed video signal is input to the monitor 206, and the monitor 206 displays a composed picture of the objects to the monitored, that is, the volcano, river, power line and factory.
The multiple picture composing apparatus 202 has a construction applied with a video editing function of a television broadcasting system, and includes the synchronizing signal distributor 202a. Although high-performance multiple picture composing apparatuses have been reduced to practice, such multiple picture composing apparatuses are expensive. In addition, the transmission units 203 and 205 respectively have a construction capable of compressing, encoding and decoding the video signal in accordance with the transmission band of the network 204, and applied with standardized means such as H.320 (H.261), MPEG1, 2, 4, MOTION-JPEG, H.324 (H.263).
In a case where each television camera is set up in a corresponding video conference room, the transmission units 203 and 205 are mutually coupled to a part of the network 204 via a multi-point connection unit. In this case, the video signal distribution is controlled so as to form a video conference system.
FIGS. 2A through 2D are diagrams for explaining the multiple picture composing, and show monitoring screens at receiving ends of a remote monitoring system. FIG. 2A shows a split monitoring screen which includes 4 split pictures and is identical to the display screen of the monitor 206 shown in FIG. 1. FIG. 2B shows a split monitoring screen which includes 3 split pictures, wherein the monitoring picture of the river shown in FIG. 2A is deleted and the monitoring picture of the factory is arranged at the position of the monitoring picture of the river. FIG. 2C shows a split monitoring screen which includes 4 split pictures and includes in addition to the monitoring pictures of the power line and the factory the monitoring pictures of the present volcano and the volcano which is picked up and recorded in the past, so as to facilitate comparison of the present volcano and the past volcano. Further, FIG. 2D shows a split monitoring screen which includes 4 split pictures and includes in addition to the monitoring pictures of the power line and the factory the monitoring pictures of the volcano and an enlarged part of the volcano such as a crater thereof.
In order to use a common picture transmission unit with respect to a plurality of terminal equipments, a system which transmits a composed multiple picture and separates the pictures at the receiving end to be transferred to corresponding terminal equipments is proposed in a Japanese Laid-Open Patent Application No.4-7990, for example. In addition, a system which writes asynchronous video signals in a common memory by carrying out an address control and composes the pictures which are divided along a vertical direction of the common memory is proposed in a Japanese Laid-Open Patent Application No.54-148426, for example.
The process of composing synchronized video signals is relatively easy since the video signals are synchronized. However, there is a problem in that the multiple picture composing apparatus which carries out such a composing process is expensive.
On the other hand, the process of composing asynchronized video signals can be realized by a less expensive multiple picture composing apparatus as compared to the case where the synchronized video signals are composed. However, it is difficult to control the composing process in such a multiple picture composing apparatus. Moreover, in the case of the proposed system which uses a common memory, the composed picture is divided along the vertical direction, and the application of the system is limited.
In addition, although the standardized means described above prescribed for the transmission system of the video signal related to the single picture is applicable to the encoding and decoding, there is a problem in that the standardized means cannot be applied automatically to the multiple picture composing process. In other words, in the case of the multiple picture composing process, the importance of the picture may differ among the pictures, and a sufficient monitoring cannot be realized by composing all of the pictures in the same manner.
Accordingly, it is a general object of the present invention to provide a novel and useful multiple picture composing method and multiple picture composing apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a multiple picture composing method for composing video signals from a plurality of video signal sources which operate asynchronously to each other, comprising the steps of (a) successively selecting the video signals from the video signal sources, (b) reading the selected video signals in units of frames while maintaining horizontal and vertical synchronization of the selected video signals, (c) reducing the video signals in the units of frames in correspondence with areas allocated for each of pictures to be composed in a composed picture, (d) writing the reduced video signal in blocks of a picture composing memory corresponding to the areas allocated for each of the pictures to be composed, and (e) composing the video signals stored in the picture composing memory to obtain a composed video signal related to a composed picture and subjecting the composed video signal to at least one of an encoding process and a transmission process. According to the multiple picture composing method of the present invention, it is possible to reduce the cost of the system by using asynchronous video signal sources. In addition, it is possible to simplify control operations by relating the picture composing process and the encoding process or the transmission process.
Still another object of the present invention is to provide a multiple picture composing apparatus for composing video signals from a plurality of video signal sources which operate asynchronously to each other, comprising a video signal selector selecting the video signals from the video signal sources, an input signal monitoring unit reading the video signals selected by the video signal selector while maintaining horizontal and vertical synchronization of the selected video signals, a horizontal direction reducer reducing the video signals synchronized by the input signal monitoring unit in units of frames in correspondence with areas allocated for each of pictures to be composed in a composed picture, a picture composing memory storing the video signals reduced by the horizontal direction reducer in units of lines, a picture composing controller controlling reading of the video signals by the input signal monitoring unit via the video signal selector and a picture composing process with respect to the video signals stored in the picture composing memory, and an encoder carrying out the picture composing process with respect to the video signals stored in the picture composing memory. According to the multiple picture composing apparatus of the present invention, it is possible to reduce the cost of the system by using asynchronous video signal sources. In addition, it is possible to simplify control operations by relating the picture composing process and the encoding process or the transmission process.
Furthermore, if the setting of the quantization value, the number of times the video signals are read, the encoding process or the like are carried out with priority with respect to the video signal of a weighted channel, it is possible to improve the sharpness or clarity of an important part of the received and displayed composed picture, and the accuracy of a remote monitoring or the like can be improved. It is also possible to utilize an invalid area on the composed picture, so as to make an enlarged display, a zoom-up display, and returning of a specific pattern or received and decoded picture. Moreover, it is possible to carry out a remote control of the multiple picture composing process by exchanging information for the remote control operation between a monitoring end and a monitored end. Accordingly, the present invention can be applied to various systems to realize an economical and efficient multiple picture composing process.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.